There is an interest in materials that can be used for electronic signage applications. Typically such applications are outdoors or in well-lit locations and emissive technologies such as LCDs exhibit increased backlight power consumption in order to overcome ambient lighting conditions. There is an advantage to be found if a low power technology can be used. One such technology is Electrophoretic Displays (EPDs). These rely on the reflection of ambient light, and are therefore ideal for conditions where the ambient light is high intensity—such as outdoors or in shops and restaurants. To use an EPD with low intensity (or without) ambient light, a front light is required, however the power consumption of front lighting is far less than that of an LCD backlight.
Particles suitable for use in electrophoretic displays (EPD), e.g. coloured electronic paper have been exemplified in recent patent literature; e.g. (U.S. Pat. No. 7,304,634, GB 2 438 436, US 2007/0268244). It is now possible to control and manipulate features such as size, colour, charge and polydispersity independently to produce particles with desired properties for EPD; e.g. WO 2010/089057. A number of different techniques can be used to create an optical effect by the movement of particles. One such method can incorporate the use of reflective colour particles, and absorbing black particles to generate a pixel that can be switched between a colour, and a black optical state.
The earlier application WO2013/189580 describes a method of using electrophoretic materials to generate high colour saturation and high reflectivity in a Black/Colour pixel by using black and white particles with a dyed solvent. This method is limited to Black vs. Colour, or 3 state pixels of Black vs. Colour vs. White.
One major drawback of EPD is that it is challenging to achieve good saturated colour, and the range of colours is limited. So, there continues to be a demand for improved electrophoretic fluids.